We have been predominantly interested in the electron during this course. In order to understand alpha radioactivity we need to become more familiar with the atom's nucleus.
The nucleus of an atom has a size of about 10-15 m or 10-6 nm. It is very tiny compared to the most probable place to find the electrons.
The nucleus has very little interaction in processes such as chemical changes, etc.
The nucleus consists of two elementary particles, the proton and the neutron. The mass of these two particles is approximately 1.7 x 10-27 kg. This is 1850 times that of the electron.
The number of protons in the nucleus determines the number of electrons in the atom. Thus the "chemical" properties of an element depend on the number of protons. Neutrons do not change the type of element. We use the term "isotopes" to describe the same element with different number of neutrons.
Notation
One proton, no neutrons
One proton and one neutron
The interactions in the nucleus are due to two different forces:
1) Electromagnetic force This is a force that acts over distances longer than the strong nuclear force described in 2) below. Protons repel each other with this force and neutrons are not affected.
2) Strong nuclear force This is a strongly attractive force that acts between all nucleons (protons and neutrons).
We never observe the following Helium isotope in nature:
Two protons, no neutrons.
For the first half of the periodic table the number of protons = number of neutrons. Then thenumber of neutrons become greater.
Why do you think we need both protons and neutrons in the nucleus?
Potential Energy Diagram for the Nucleus To draw such a diagram we need to consider the two forces: 1) Strong attraction at short range (0.0004 to 0.001 nm) 2) Repulsion at extremely close range (<0.0004 nm)
Describe how these forces will affect neutrons.
Describe how these forces will affect protons.
Have a look at the two potential energy diagrams in Figure 1. Which of the two would be an appropriate potential energy diagram for neutrons? How about protons? Explain why you made those choices below.